Let S Get Ready for Chapter 9 Testing Hypothesis

LET’S GET READY FOR CHAPTER 9 – TESTING HYPOTHESIS

Complete pages 1, 2, 3, 5. READ page 4 many times to understand the problems – DUE Thursday 4/16

1)X~N(mu = 0, sigma = 1)

We select a random sample of size 10 from this population.

a)Describe the distribution of sample means for samples of size 10 (justify shape). Round the standard deviation to two decimal places.

b)Sketch the distribution of sample means labeling on the axis the values of the mean and 1, 2, 3 standard deviations on either side of the mean.

c)Suppose we select a sample of size 10 and we observe an x-bar of 0.3. Locate x-bar = 0.3 on the graph from part (b) and select one of the following:

x-bar = 0.3 can easily occur by chance when mu = 0

x-bar = 0.3 would rarely occur just by chance if mu = 0

d)Suppose we select a sample of size 10 and we observe an x-bar of 1.02. Locate x-bar = 1.02 on the graph from part (b) and select one of the following:

x-bar = 1.02 can easily occur by chance when mu = 0

x-bar = 1.02 would rarely occur just by chance if mu = 0

e)If we select a sample of size 10 from the population, what is the probability that x-bar is 0.3 or more?

f)If we select a sample of size 10 from the population, what is the probability that x-bar is 1.02 or more?

2)X ~ N (mu = 18, sigma = 4.2)

We select a random sample of 45 numbers from this population.

a)Describe the distribution of sample means for samples of size 45 (justify shape). Round the standard deviation to two decimal places.

b)Sketch the distribution of sample means labeling on the axis the values of the mean and 1, 2, 3 standard deviations on either side of the mean.

g)Suppose we select a sample of size 45 and we observe an x-bar of 17.2. Locate x-bar = 17.2 on the graph from part (b) and select one of the following:

x-bar = 17.2 can easily occur by chance when mu = 18

x-bar = 17.2 would rarely occur just by chance if mu = 18

h)Suppose we select a sample of size 45 and we observe an x-bar of 14.68. Locate x-bar = 14.68 on the graph from part (b) and select one of the following:

x-bar = 14.68 can easily occur by chance when mu = 18

x-bar = 14.68 would rarely occur just by chance if mu = 18

i)If we select a sample of size 45 from the population, what is the probability that x-bar is 17.2 or less?

j)If we select a sample of size 45 from the population, what is the probability that x-bar is 14.68 or less?

SIMULATION of problem 1

Let’s simulate selecting a sample of size 10 from a normal population with mean 0 and standard deviation of 1.

RandNorm(0, 1, 10)→L1: mean(L1) ENTER

Do this process 10 times (by pressing ENTER 10 times). Round the sample means to 3 decimal places

x-bar
Is it ≥ 0.3?
Is it ≥ 1.02?

We’ll collect class results here:

SIMULATION of problem 2

Let’s simulate selecting a sample of size 45 from a normal population with mean 18 and standard deviation of 4.2.

RandNorm(18,4.2,45)→L1: mean(L1) ENTER

Do this process 10 times (by pressing ENTER 10 times). Round the sample means to 3 decimal places

x-bar
Is it ≤ 17.2?
Is it ≤ 14.68?

We’ll collect class results here:

HERE WE HAVE THE REAL STORY for all the numbers we have been using on problem 1

Diet colas use artificial sweeteners to avoid sugar. These sweeteners gradually lose their sweetness over time. Manufacturers therefore test new colas for loss of sweetness before marketing them. Trained tasters sip the cola along with drinks of standard sweetness and score the cola on a “sweetness score” of 1 to 10. The cola is then stored for a month at high temperature to imitate the effect of four months storage at room temperature. Each taster scores the cola again after storage. This is a matched pairs experiment. Our data are the differences (score before storage minus score after storage) in the taster’s scores. The bigger these differences, the bigger the loss of sweetness

Suppose we know that for any cola, the sweetness loss scores vary from taster to taster according to a Normal distribution with standard deviation sigma = 1. The mean mu for all tasters measures loss of sweetness and is different for different colas.

Here are the sweetness losses for a new cola, as measured by 10 trained tasters:

2.0, 0.4, 0.7, 2.0, -0.4, 2.2, -1.3, 1.2, 1.1, 2.3

Most are positive. That is, most tasters found a loss of sweetness,(Sweetness before – sweetness after > 0) and two tasters thought the cola gained sweetness. (Sweetness before – sweetness after < 0)

The average sweetness loss is given by the sample mean x-bar = 1.02. Are these data good evidence that the cola lost sweetness in storage?

If we select a sample of size 10 from this population and observe an x-bar of 0.3, what is the value of this x-bar suggesting about the sweetness of cola?

If x-bar = 0.3, it is clear that an x-bar this large could easily occur just by chance when the population mean is mu = 0. That 10 tasters found x-bar = 0.3 is not evidence that this cola loses sweetness.

If we select a sample of size 10 from this population and observe an x-bar of 1.02, what is the value of this x-bar suggesting about the sweetness of cola?

The taste test for the new cola produced x-bar 1.02. That’s way out on the Normal curve, so far out that an observed value this large would rarely occur just by chance if the true mu were 0. This observed value is good evidence that the true mu is in fact greater than 0, that is, that the cola lost sweetness. The manufacturer must reformulate the cola and try again.

HERE WE HAVE THE REAL STORY for all the numbers we have been using on problem 2

The Food and Nutrition Board of the National Academy of Sciences states that the recommended daily allowance (RDA) of iron for adult females under the age of 51 is 18 mg. Assume that the population standard deviation is sigma = 4.2 mg.Are adult females under the age of 51 on average getting less than the RDA of 18 mg. of iron?

If we select a sample of size 45 from this population and observe an x-bar of 17.2, what is the value of this x-bar suggesting about the daily iron intake of women under the age of 51?

The graph shows that an x-bar = 17.2 could easily occur just by chance when the population mean mu = 18. In this case, there is no evidence that adult females under the age of 51 are, on average, getting less than the Recommended Daily Allowance of 18 mg. of iron.

If we select a sample of size 45 from this population and observe an x-bar of 14.68, what is the value of this x-bar suggesting about the daily iron intake of women under the age of 51?

Since 14.68 it is so far out on the Normal curve, this observed value would rarely occur just by chance if the true mu were 18. This observed value is good evidence that the true mu is in fact lower than 18. There is evidence that adult females under the age of 51 are, on average, getting less than the RDA of 18 mg. of iron.

Problem 2 – continued

There is real data collected about the daily iron intake of 45 women under 51 years of age, with a sample mean x-bar of 14.68 mg. We have seen that if the mean of the population is 18, it is VERY UNLIKELY to select a sample of size 45 and observe an x-bar of 14.68 or less.

Either SOMETHING VERY RARE HAPPENED or, in reality THE MEAN OF THE POPULATION IS LOWER THAN 18.

In statistics, we tend to conclude that probably the mean of the population is lower than 18.

If we think that the mean of the population is lower than 18, let’s construct a 95% confidence interval estimate to have an idea what the population mean could be. (Use x-bar = 14.68, sigma = 4.2, and n = 45) – Show formulas and then check with a calculator feature.

To understand more the situation, let’s simulate again

We really don’t know what the population mean is; but with 95% confidence we can say that it is

between ______and ______

For simulation purposes we need to have a value for mu, so we are going to assume mu is 15 (since 15 is one of the numbers on the interval obtained above) and use it in the simulation of the random selection.

RandNorm(15,4.2,45)→L1:mean(L1) ENTER

Record the obtained mean. Press ENTER again, and record the mean. Do this 5 times.

Do you realize that now a sample mean of 14.68 or less is MORE LIKELY?

Let’s see how this problem 2 will be phrased on chapter 9 – We’ll do together in class.

A hypothesis test is to be performed to decide whether adult females under the age of 51 are, on average getting less than the RDA of 18 mg. of iron.

A random sample of 45 adult women under 51 was selected and the iron intake (in mg.) during a 24-hour period was obtained giving a sample mean of 14.68 mg.

At the 5% significance level, do the data suggest that adult females under the age of 51 are, on average, getting less than the RDA of 18 mg. of iron?